Can Falcon 40B Instruct run on RX 7900 XT 20GB?

YES — With Q2_K

B70Good

○Estimated from fit model

Falcon 40B Instruct needs ~20.6 GB VRAM. RX 7900 XT 20GB has 20.0 GB. With Q2_K quantization, expect ~20 tok/s.

Runtime: OllamaCapacity: OffloadBandwidth: HighStack: BasicBottleneck: Balanced

Operating mode

Choose the run profile you care about

Interactive favors responsiveness, while light API and scale-out lean harder on serving readiness. The fit stays the same, but the recommendation lens changes.

Current mode

Balanced

Balanced for general local use. Keeps the ranking neutral across personal and serving workflows.

Falcon 40B Instruct at Q5_K_M needs 33.8 GB — too much for RX 7900 XT 20GB (20.0 GB). Runs at Q2_K (20.6 GB) with low quality.

Capabilities:

Select quantization to explore

Q5_K_M (High quality) — 33.8 GB, exceeds 20.0 GB available

33.8 GB required20.0 GB available

169% VRAM needed

13.8 GB over capacity — needs offload or smaller quantization

Fit status

Too heavy

Decode

4.6 tok/s

TTFT

42219 ms

Safe context

Memory

33.8 GB / 20.0 GB

Offload

40%

Memory breakdown

Weights28.8 GB

KV Cache1.8 GB

Runtime1.2 GB

Headroom2.0 GB

See how fast it feels

With memory offload — actual speed may be lower

See how fast it feelsFalcon 40B Instruct on RX 7900 XT 20GB
1st promptCold start — includes initialization
>Solve: If a train travels at 60 mph for 2.5 hours, how far does it go?
Let me work through this step by step.

Given information:
 - Speed = 60 mph (miles per hour)
 - Time = 2.5 hours

Formula: Distance = Speed x Time

Calculation:
 Distance = 60 mph x 2.5 h
 = 150 miles

The train travels 150 miles.

Double-check: at 60 mph the train covers 60 miles each hour. In half an hour it covers 30 miles. So in 2.5 hours: 60 + 60 + 30 = 150 miles. Confirmed.
2nd promptWarm — model ready, no init overhead
>What if the train stops for 20 minutes halfway?
The stop doesn't change the total distance covered while moving, but it affects total trip time.

Breakdown:
 - First half: 1.25 hours at 60 mph = 75 miles
 - Stop: 20 minutes (no distance)
 - Second half: 1.25 hours at 60 mph = 75 miles

Total distance: 150 miles (same)
Total time: 2.5 h + 0.33 h = 2.83 hours
Average speed: 150 / 2.83 = 53 mph

The distance stays the same but average speed drops to 53 mph because of the stop.
Estimated: 4.6 tok/s decode · 42.2s TTFT (warm) · 12 tok/s prefill

What limits this setup

This setup is broadly balanced for this model.

Very little memory headroom

You can run the model, but there is not much room left for longer context, bigger batches, extra apps, or future model updates.

Best improvement path

Buy headroom, not only minimum fit

A slightly larger memory tier gives you safer context growth and makes the recommendation more future-proof.

Performance by workload

Workload	Grade	Fit	Decode	TTFT	Context
Chat	F	Too heavy	4.9 tok/s	21736 ms	4K
Coding	F	Too heavy	4.6 tok/s	42219 ms	4K
Agentic Coding	F	Too heavy	4.1 tok/s	68615 ms	4K
Reasoning	F	Too heavy	4.6 tok/s	49895 ms	4K
RAG	F	Too heavy	4.1 tok/s	85769 ms	4K

Quantization options

How Falcon 40B Instruct (40B params) fits at each quantization level on RX 7900 XT 20GB (20.0 GB usable).

Quant	Bits	VRAM	Quality	Fit
Q2_K	2	15.6 GB	Low	F0
Q3_K_S	3	19.6 GB	Low	F0
NVFP4	4	22.4 GB	Medium	F0
Q4_K_M	4	24.4 GB	Medium	F0
Q5_K_M	5	28.8 GB	High	F0
Q6_K	6	32.8 GB	High	F0
Q8_0	8	42.8 GB	Very High	F0
F16	16	82.0 GB	Maximum	F0

Get started

Copy-paste commands to run Falcon 40B Instruct on your machine.

Run

docker run --rm -it ghcr.io/ggerganov/llama.cpp:full \
 --hf-repo "tiiuae/falcon-40b-instruct" \
 --hf-file "falcon-40b-instruct-Q5_K_M.gguf" \
 -c 4096 -ngl 99

Upgrade options